Re: Fwd: Re: Using netCDF-Java to change an attribute value without rewriting the file

Ethan Davis wrote:
> Changing attribute _names_ without re-writing the file?
>
> Ethan
>
> -------- Original Message --------
> Subject: Re: Using netCDF-Java to change an attribute value without
> rewriting the file
> Date: Wed, 17 Feb 2010 12:27:45 -1000
> From: Ted Habermann <address@hidden>
> To: Ethan Davis <address@hidden>
>
> Thanks Ethan, what about attribute names?
>
> Ted
>
> On Feb 17, 2010, at 11:55 AM, Ethan Davis <address@hidden>
> wrote:
>
> > Hi Ted,
> >
> > I just checked with John on this. The netCDF-Java library supports
> > changing attribute values on an existing netCDF file; there are two
> > situations where the file will NOT have to be rewritten:
> >
> > 1) The new attribute value is shorter than or equal in length to the  
> > old
> > attribute.
> >
> > 2) The netCDF file has enough padding at the end of the header section
> > to accommodate the extra length of the attribute value.
> >
> > Otherwise, the entire file will need to be rewritten.
> >
> > Ethan

on NetcdfFileWriteable:

 public Attribute renameVariableAttribute(String varName, String attName, 
String newName) {
 public Attribute renameGlobalAttribute(String oldName, String newName) {

the file must be rewritten when the header can no longer fit in the allocated 
space. One can reserve more space upon creation with

 /**
  * Set extra bytes to reserve in the header.
  * This can prevent rewriting the entire file on redefine.
  * Must be in define mode
  * @param extraHeaderBytes # bytes extra for the header
  */
 public void setExtraHeaderBytes(int extraHeaderBytes) {